Subjective tones: Growth of 2f1+fh and fh+f1 for independently varied primary amplitudes

Abstract

Two nonlinear amplitude distortion mechanisms have recently been proposed as explanations of the generation of aural combination tones. One, a polynomial power series, predicts combination tones which grow at an accelerated rate in comparison with the increased stimulus amplitudes. The second, an essential nonlinearity, predicts distortion product relative levels independent of stimulus amplitude. In a past study [J. Erdreich and T.D. Clack, J. Acoust. Soc. Am. 55, S7–S8 (1974)], it was shown that only when a combination tone becomes audible and presumably subject to modification by perceptual processes does it grow at nonaccelerated rates. The current study examines the growth of the cubic summation tone 2f1+fh and the quadratic sum tone fh+f1(fh/f1=1.2, f1=1 kHz) as the level of each primary is varied independently. It is found that the accelerated distortion product growth rate conforms with the predictions of the power-series nonlinearity hypothesis. [Supported in part by grant from Sigma Xi.]